1. Field of the Invention
The present invention relates generally to methods of determining an object's position and, in a preferred embodiment thereof, more particularly provides a method and apparatus for optically digitizing an object's position on a plane above a computer keyboard.
2. Description of Related Art
Pointing devices are well known in the computer art. Their purpose, generally, is to permit the computer user to input positional information to the computer. A pointing device performs this function by "digitizing" an object's relative position in space, that is, by putting the positional information in a form that is readable by the computer.
The number of uses for pointing devices have increased as modern computer user interfaces have become increasingly graphical. For example, a computer user may now use a "mouse" to select a file to open for editing purposes (by "clicking" on an icon representing the file), instead of typing a file name on a keyboard.
Typical pointing devices currently available to computer users include mouse, trackball, digitizing pad, joystick, touch screen, and eye tracking devices. There are variations of each of these and there are pointing devices that have a combination of features found on more than one of these. Each, however, has its disadvantages.
A mouse typically has a housing for grasping in the user's hand, and a ball underneath the housing for rolling the housing about on a desktop. Rollers inside the housing digitize the mouse's position by translating the ball's movement into electrical signals which are then communicated to the computer. Switches, typically mounted to the housing's top surface, allow the user to "click" (activate a switch to select an icon, for example) on an object displayed on the computer's screen, or perform other functions. The mouse, however, requires the user to devote a significant portion of a desktop as an area in which the mouse can be rolled around. The mouse also requires the user to remove one hand from the keyboard while the mouse is being rolled around on the desktop and/or while a mouse switch is being activated, thus slowing down the data entry process. Furthermore, the mouse requires a means of communicating the electrical signals to the computer, such as a cable which must be attached between the computer and the mouse and must follow the mouse around the desktop.
A trackball eliminates some of the mouse's disadvantages, but substitutes others in their place. The trackball is, essentially, an upside-down mouse, having a stationary housing with the ball facing upward so that the ball can be rolled by the user's fingers. The switches are normally placed on the top surface of the housing adjacent the ball. The rollers which translate the ball's motion into electrical signals are located in the housing where, due to the large upward-facing opening in the housing through which the ball protrudes, they are exposed to dust and dirt. Some keyboard manufacturers have eliminated the need for a separate trackball device cable for communicating the electrical signals to the computer by building the trackball device directly into the keyboard housing so that a single cable communicates both keyboard and trackball input to the computer. The user does, however, still have to move his or her hand away from the keyboard in order to roll the ball. Another disadvantage is that a large amount of dexterity is required to manipulate the trackball while clicking on a screen object, if only one hand is used.
A digitizing pad typically utilizes a rectangular planar area on the surface of a hard plastic housing, which, in turn, is placed on the user's desktop. The pad uses one of several methods to sense the position of a pen or stylus on the pad surface. In some pads, the pressure of the pen or stylus on the pad surface makes contact or changes capacitance in many fine, closely spaced conductors beneath the pad's surface. In some others, the pen or stylus carries a magnetic or electromagnetic field source which is sensed by the pad, thus, the pen or stylus position is sensed due to the proximity of the pen or stylus to the pad. Among the digitizing pad's disadvantages is the space on the desktop taken up by the pad's housing. Additionally, the user must remove his or her hand from the keyboard to operate the pen or stylus.
A joystick is another pointing device, and may have either a movable or a non-movable stick. The movable joystick operates similar to a trackball, except that a stick is inserted into the ball giving the user a means of grabbing the ball. The stick also limits movement of the ball. The non-movable joystick utilizes pressure sensors encircling the stick to sense the force and direction in which the user is pushing the stick. Thus, the non-movable joystick does not communicate a position to the computer, instead it senses a force vector which the computer may use to adjust the position of a screen object. As joysticks rely upon a translation of a sensed force vector into a change in cursor position, joystick manipulations are often counterintuitive to computer users. Thus, in comparison with other pointing devices, joysticks have a significant problem in ease of use.
Eyetracking devices use expensive, sophisticated methods of determining where on the computer screen the user's eyes are focuses. In this way the user's hands do not have to leave the keyboard in order for the positional information to be communicated to the computer. Unfortunately, however, this technology is not within financial reach of most computer users.
Touch screens permit the user to communicate a position to the computer by actually touching an area on the computer screen. Usually the screen area is associated with an object or menu choice displayed on the screen. As with all of the aforementioned pointing devices, with the exception of the eyetracking devices, the user's hand must leave the keyboard to use the device.
From the foregoing, it can be seen that it would be quite desirable to provide a method of communicating an object's position to the computer which does not require the removal of either of the user's hands from the keyboard and which may be economically produced. It is accordingly an object of the present invention to provide such a method and associated apparatus.